The present invention relates to an apparatus for non-destructively inspecting a heat exchanger tube and a group of heat exchanger tubes, and more particularly to an apparatus for inspecting a heat exchanger tube or a group of heat exchanger tubes for a defect by imaging a cross section thereof by CT (Computed Tomography) processing by utilizing radiations. This technique is suitably applied to the diagnosing of a defect of a heat exchanger tube used in, for example, a heat exchanger, a steam generator, a boiler and the like.
A heat exchanger and a steam generator and the like generally have a structure in which a group of heat exchanger tubes constructed by arranging and bundling a multiplicity of heat exchanger tubes are incorporated in a container. The use of these heat exchanger tubes under severe conditions for a long period of time gives rise to a fear of the occurrence of various kinds of defects therein. Therefore, it is necessary to carry out a non-destructive inspection of heat exchanger tubes periodically, or at any time as the occasion demands.
Typical non-destructive inspection methods which have heretofore been carried out in practice include a visual inspection method, an ultrasonic wave inspection method, an eddy current inspection method and the like. The visual inspection method is a method of inserting an optical device, such as a reflecting mirror, a camera and the like in the vicinity of an object to be inspected, and observing the object directly or indirectly. The ultrasonic wave inspection method is a method of conducting flaw detection, thickness measurement and the like by sending an ultrasonic pulse toward an object to be inspected, receiving a reflected wave from an interface, etc. of the object, converting the received wave into an electric signal, and continuing observation of the electric signal for a given length of time. The eddy current inspection method is a method of determining the existence or non-existence of a defect and measuring the thickness of an object by supplying an AC current to a test coil, and detecting an eddy current induced by the object to be inspected, with reference to the variation of impedance of the coil. These non-destructive inspection methods are usually carried out from the inner side of a heat exchanger tube for the reason that the accessing to the object to be inspected is done easily.
However, these inspection methods have various problems that only an inner surface of the heat exchanger tube can be inspected, that a double tube or a triple tube having a clearance between an outer tube member and an inner tube member cannot be inspected, that a tube made of a magnetic material is difficult to inspect, and the like. Therefore, these inspection methods have to be selectively used in accordance with the material, construction and a portion of the heat exchanger tube to be inspected. As a result, an inspecting operation cannot be carried out fully satisfactorily in some cases, and an inspecting operation becomes complicated in other cases.
Further, these prior art inspection methods are directed to a single heat exchanger tube only, and are incapable of observing the whole of a group of heat exchanger tubes and diagnosing various kinds of defects thereof.
An object of the present invention is to provide an apparatus capable of non-destructively and easily inspecting a heat exchanger tube and a group of heat exchanger tubes for a defect, a wall thickness and the like regardless of the material and construction of the heat exchanger tube or of the condition of arrangement of a multiplicity of heat exchanger tubes.
According to the present invention, there is provided an apparatus for non-destructively inspecting an arbitrary heat exchanger tube among a group of heat exchanger tubes in which a multiplicity of heat exchanger tubes are arranged. The apparatus comprises a radiation detector inserted in a heat exchanger tube to be inspected, at least one radiation source inserted in a plurality of heat exchanger tubes surrounding the heat exchanger tube to be inspected, and a CT processing unit for subjecting radiation strength signals detected by the radiation detector to a CT processing, whereby a cross section of the heat exchanger tube to be inspected is imaged by the CT processing.
As heat exchanger tubes in which the radiation source is to be inserted, it is most simple to select heat exchanger tubes adjoining the heat exchanger tube to be inspected. However, as long as the radiation detector in the heat exchanger tube to be inspected can detect radiations transmitted through the heat exchanger tubes, the radiation source may be inserted in a heat exchanger tube disposed away from the heat exchanger tube to be inspected with other heat exchanger tubes interposed therebetween.
According to the present invention, there is also provided an apparatus for non-destructively inspecting an arbitrary heat exchanger tube among a group of heat exchanger tubes in which a multiplicity of heat exchanger tubes are arranged. The apparatus comprises a radiation detector inserted in a heat exchanger tube to be inspected, at least one radiation source set in the interior of a plurality of heat exchanger tubes and additionally disposed simulated heat exchanger tubes surrounding the heat exchanger tube to be inspected, and a CT processing unit for subjecting radiation strength signals detected by the radiation detector to a CT processing, whereby a cross section of the heat exchanger tube to be inspected is imaged by the CT processing.
The simulated heat exchanger tube may be, for example, a tubular body having the same outer shape and formed of the same material as the heat exchanger tube. The additional disposition of the simulated heat exchanger tubes is especially effective in the case where the heat exchanger tube disposed on the circumferentially outermost portion is inspected.
According to the present invention, there is further provided an apparatus for non-destructively inspecting an arbitrary heat exchanger tube among a group of heat exchanger tubes in a nuclear reactor plant in which a multiplicity of heat exchanger tubes are arranged. The apparatus comprises a radiation detector inserted in a heat exchanger tube to be inspected and a CT processing unit for subjecting radiation strength signals detected by the radiation detector to a CT processing, whereby radiations emitted from radioactive nuclides produced in a nuclear reactor coolant are detected by the radiation detector, and a cross section of the heat exchanger tube to be inspected is imaged by the CT processing.
When a group of heat exchanger tubes (for example, a heat exchanger, a steam generator and the like) are incorporated in a nuclear reactor plant, it is possible to directly utilize radiations emitted from radioactive nuclides (for example, sodium-22, sodium-24 and the like) in a coolant as a radiation source. These radioactive nuclides in the coolant are produced by nuclear reactions of coolant sodium and neutrons in the nuclear reactor.
According to the present invention, there is also provided an apparatus for non-destructively inspecting a group of heat exchanger tubes in which a multiplicity of heat exchanger tubes are arranged. The apparatus comprises at least one radiation source set in at least one of the positions selected from a position in an inner portion of the heat exchanger tube, a position on the inner side of the group of heat exchanger tubes or a position on the outer side of the group of heat exchanger tubes, at least one radiation detector carrying a collimator set in a position on the outer side of the group of heat exchanger tubes so that radiations emitted from the radiation source can be detected by the collimator-carrying radiation detector over substantially the whole circumference of the group of heat exchanger tubes, and a CT processing unit for subjecting radiation strength signals detected by the collimator-carrying radiation detector to a CT processing, whereby a cross section of the group of heat exchanger tubes is imaged by the CT processing.
According to the present invention, there is further provided an apparatus for non-destructively inspecting a group of heat exchanger tubes in a nuclear reactor plant in which a multiplicity of heat exchanger tubes are arranged, The apparatus comprises at least one radiation detector carrying a collimator set in a position on the outer side of the group of heat exchanger tubes so that radiations can be detected by the collimator-carrying radiation detector over substantially the whole circumference of the group of heat exchanger tubes, and a CT processing unit for subjecting radiation strength signals detected by the collimator-carrying radiation detector to a CT processing, whereby radiations emitted from radioactive nuclides produced in a nuclear reactor coolant are detected by the collimator-carrying radiation detector, and a cross section of the group of heat exchanger tubes is imaged by the CT processing.
A multiplicity of collimator-carrying radiation detectors may be set on the outer side of the group of heat exchanger tubes at substantially uniform intervals over substantially the whole circumference of the group of heat exchanger tubes. Alternatively, a single or a plurality of collimator-carrying radiation detectors may be set on the outer side of the group of heat exchanger tubes so that the collimator-carrying radiation detector can be moved in the circumferential direction of the group of heat exchanger tubes. In either case, transmission strength data of radiations can be obtained over the whole circumference of the group of heat exchanger tubes.
The xe2x80x9cCTxe2x80x9d generally means a method of obtaining a cross-sectional image of an object to be inspected by calculation based on measured values of projection amounts in various directions by utilizing X-rays, ultrasonic waves, various kinds of corpuscular rays and the like. In the present invention, radiations (X-rays or xcex3-rays) are utilized. The radiations sent out from radiation sources placed in various positions transmit an object to be inspected, and the transmitted radiations are detected by the radiation detector. Signals obtained by detecting the transmitted radiations are subjected to calculation in a computer, and the object to be inspected is thereby restructured as a cross-sectional image, which is then displayed.
In the present invention, when a driving mechanism capable of moving one or both of the radiation source and the radiation detector in the axial direction of the heat exchanger tube is provided, inspecting the heat exchanger tube in the axial direction thereof becomes possible. In the case of the group of heat exchanger tubes incorporated in the nuclear reactor plant, by providing a driving mechanism capable of moving the radiation detector in the axial direction of the heat exchanger tube, the inspection of the heat exchanger tube in the axial direction thereof becomes possible. As a result, it is possible to obtain cross-sectional images of the whole length of the heat exchanger tube or the group of heat exchanger tubes, continuously throughout the length thereof or intermittently at desired intervals of the length thereof.